AC to DC converters are frequently used to provide power from an AC power supply to one or more devices which require DC power. In some applications, AC to DC converters are used to provide DC power to a DC to AC converter. In such applications, the AC to DC converter and the DC to AC converter collectively form an AC to AC inverter. FIG. 1 illustrates a system 100 including an AC to DC converter 120 providing power from AC service 115 to an AC motor 180 via the DC to AC converter 130.
In some cases, the AC service 115 can have power quality requirements, such as those specified by Mil-Std-1399 Sec. 300B, or other power quality standards. In such cases, harmonics generated by the AC to DC converter 120 should be minimized, as they may cause the voltage of the AC service 115 to deviate from a pure sinusoid. These deviations may cause poor performance in other devices connected to the AC service 115. In addition, these deviations may cause the AC service 115 to fail the power quality requirements.
AC to DC Converters may utilize pulse-width modulated current source rectifiers, such as that shown in FIG. 2, as opposed to passive rectifiers, thyristor-based phase controlled rectifiers and voltage source rectifiers. The current source rectifier is an attractive alternative to these other types of rectifiers more widely used by industry because it can achieve AC-to-DC voltage conversion with nearly sinusoidal input currents with less input filter components, no in-rush limiting circuitry and no step-down transformer in cases where the desired output voltage is lower than the input. All of this results in smaller size and lower parts count.
The current source rectifier 110 shown in FIG. 2A is an active AC-to-DC rectifier that converts three-phase AC input power to a controlled DC voltage through an active rectification process and drives a constant power load 104. In the illustration, the three-phase AC input power is shown coming off of an AC power grid 102 and is provided to the current source rectifier 110 through input lines a, b, and c. The controller 101 receives the input voltages via signal drivers 106 and 108. The controller 101 also receives output voltage vo as well as the DC link current ip through the inductor LP from the current source rectifier 110. Controller 101 then provides control signals Ui1-Ui6 to control the switches Si1-Si6 of the current source rectifier 110, respectively.